LR745

Features

Accepts inputs from 35V to 450V

Output current limiting

For PWM ICs with start-up threshold voltage of

13.9 - 18.0V

Very low power consumption after start-up

Applications

Notebook and laptop computers

Telecommunication power supplies

Battery chargers

Motor controllers

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General Description

The Supertex LR745 is a high input voltage SMPS start-

up circuit. The LR745 is ideally suited for use with industry

standard low voltage PWM ICs having start thresholds of 13.9

- 18.0V. It allows the PWM ICs to be operated from rectified

120 or 240VAC lines, and eliminates the use of power resistors

often used for this purpose.

The internal circuitry of the LR745 allows the PWM ICs to

operate at a V

after start-up. The auxiliary voltage can be less than the

start threshold voltage, which allows for improved efficiency.

Current from the high voltage line is drawn only during the

start-up period. After start-up, the internal high voltage line is

disconnected from the IC, thereby reducing the continuous

power dissipation to a minimum.

High Input Voltage SMPS Start-up

Ordering Information

Device

Package Options

TO-92

TO-243AA (SOT-89)

LR745

LR745N3-G

LR745N8-G

-G indicates package is RoHS compliant (‘Green’)

Absolute Maximum Ratings

Parameter

Value

Input voltage

450V

Output voltage

25V

Operating and storage temperature

Soldering temperature*

Absolute Maximum Ratings are those values beyond which damage to the device

may occur. Functional operation under these conditions is not implied. Continuous

operation of the device at the absolute rating level may affect device reliability. All

voltages are referenced to device ground.

* Distance of 1.6mm from case for 10 seconds.

Pin Configurations

GND

VIN

VOUT

VIN

VOUT

GND

GND

TO-92 (N3)

TO-243AA (SOT-89) (N8)

TO-243AA (SOT-89) (N8)

Y = Last Digit of Year Sealed

W = Code for Week Sealed

L = Lot Number

= “Green” Packaging

Si

LR

7 4 5

Y W L L

TO-92 (N3)

= “Green” Packaging

Package Markings

Package may or may not include the following marks: Si or

Package may or may not include the following marks: Si or